The joining of components by means of ultrasound is known from the prior art. The use of an ultrasonic welding process is particularly advantageous for joints with aluminium, as an aluminium oxide layer is broken up when welding with ultrasound. Due to the increasing use of aluminium stranded conductors in automotive applications, ultrasonic welding is becoming more and more popular.
In ultrasonic welding, the workpieces, in particular a stranded wire and a connecting part, are pressed together by means of a sonotrode and an anvil. The anvil as a passive tool serves in particular together with hold-down devices as a support and for fixing and/or holding down a first workpiece. The sonotrode as an active tool presses the second workpiece against the first workpiece and introduces an ultrasonic oscillation into the workpieces. Due to the ultrasonic oscillation introduced via the sonotrode, the required welding energy is generated at the connection point between the workpieces, e.g. the stranded conductor and the connecting part, in order to melt their joining partners and to connect the workpieces to each other in a material-locking manner.
However, the disadvantage of the prior art process is that only the sonotrode as an active tool introduces welding energy into the materials to be joined. The anvil is regularly mounted statically as a passive tool and does not perform any movement of its own during ultrasonic welding. This results in the sonotrode introducing welding energy only on one side into the materials to be joined. This, however, only one-sided energy input can result in the strands of the stranded cable coming into contact with the sonotrode being damaged, especially when welding stranded cables, especially with larger cross-sections. The outer strands of the stranded conductor, which serve as a coupling surface for the energy input, can be damaged during the prior art process. This leads to the disadvantage that stranded conductors can only be welded with smaller cross-sections using ultrasound without damage. Stranded cables with larger cross-sections, for example over 16 mm2, can be damaged, especially if higher welding energy is introduced into the first strand layer. Especially when joining stranded conductors with larger cross-sections, the required mechanical strength of the material-locking connection can no longer be guaranteed.
For this reason, the subject matter was based on the task of providing an ultrasonic welding device and a process for ultrasonic welding, which would enable reliable connections of stranded wires of larger cross-section with connecting parts.